Small carnivore coprolites from the Late Triassic of southern Brazil: paleobiological implications.

SOARES, MARINA B.; SCHULTZ, CESAR L.; MARTINELLI, AGUSTÍN G.; FONSECA, PEDRO HENRIQUE M.; PAES NETO, VOLTAIRE DUTRA

Brisbane

Congreso; 79th Annual Meeting, Society of Vertebrate Paleontology; 2019

A remarkable fauna is recorded in early Norian beds (ca. 225.42±0.37Ma)from the municipality of Faxinal do Soturno, State of Rio Grande do Sul,Brazil. This is mainly composed by small-sized vertebrates (maximum bodylength around 200-250 mm), such as probainognathian cynodonts,rhynchocephalians, non-rhynchocephalian lepidosauromorphs andprocolophonians. The only relatively large animal found there is thesaurischian Guaibasaurus (ca. 2m). The fossils occur in massive sandy lensesinterpreted as a fluvial/deltaic system. In this same level, more than 80elliptical coprolites, resembling rodentian feces, were found. They exhibit awhitish color and range from 7 to 10mm long and 3 to 5mm in diameter. Eightisolated coprolites were analyzed chemically and by microscopy. The x-raydiffractometry indicated quartz, plagioclase, smectite and apatite with majorpick, consistent with carnivore coprolitic materials. Thin section analysesshowed a massive coprofabric bearing sand (quartz) grains and bone remains.Micro-CT images were obtained from a sandy block with seven ?in situ?coprolites. Inside each one, a dense amount of millimetric bone elements wasrevealed compound about 40-70% of the total volume. All bones aredisarticulated. Some are complete, but the most part fragmented. Few signs ofchemical corrosion (pits) are present. Among the identifiable elements areindeterminate long bones, ribs, phalanx, and parts of neural arches of therhynchocephalian Clevosaurus brasiliensis. Although it is difficult to assignthese coprolites unequivocally to a specific producer, their measurements arein accordance with the sizes of the aforementioned small tetrapods. Theevidences point out to a strict carnivore producer with some ability of chewingbone and with fast digestion, which refers to a more mammalian physiologythan a reptilian one. The sand inside the coprolites is suggestive of soilingestion during feeding to obtain nutrients, as commonly practiced by currentfossorial animals, or just accidental ingestion. Therefore, we defend theprobainognathian cynodonts may be the potential candidates. This iscorroborated by their sectorial postcanine teeth with a more effectiveocclusion, enabling chewing movements, and features suggestive offossoriality, like a robust humerus and hypertrophied rodent-like lowerincisors (e.g., Irajatherium, Riograndia). This unprecedented Triassic recordconstitutes a rich ichnologic data source that contributes for a betterunderstanding of the initial steps of the mammalian paleobiology.